CSIS 4823 Data Communications Networking - Telecommunications

1. CSIS 4823Data Communications Networking - Telecommunications Mr. Mark Welton

2. Telecom Infrastructure • Most telecom infrastructure that exists today is based on standards more than 100 years old • Telecom infrastructure is often so reliable that we expect reliable phone service more than reliable Internet service or power

3. What is telecom? • Telecommunications refers to the traditional circuit-based switching technologies primary used by voice services • data communications often refers to packet-based switching of the modern Internet

4. Telecommunications Terms • ACD – automatic call distribution • An ACD is usually found in a call center, where calls may come in from anywhere and need to be directed to the next available operator or queued until one is available

5. Telecommunications Terms • Add/Drop – used to describe the capability of peeling off channels from a circuit for another use • An add/drop CSU/DSU can separate ranges of channels, thus allowing a T1 to be split for both voice and data use or as two partial T1s

6. Telecommunications Terms • analog in telecom refers to a signal that is continuous in amplitude and time, any small fluctuation of the signal is important • Radio waves, power waves, and sound waves are analog • When you speak, you create waves of air that hit people’s eardrums

7. Telecommunications Terms • Digital refers to a signal that has discrete values • If you analyze a sound wave, and then assign a value to each sample of the wave at specific time intervals, you will create a digital representation of the analog wave

8. Telecommunications Terms • Bandwidth vs. throughput • A range of frequencies is called a band • The width of the band is referred to as bandwidth • US FM channels run from 87.8 MHz to 107.9 MHz • The bandwidth is 20MHz

9. Telecommunications Terms • On a digital link what is referred to as bandwidth is really throughput • Throughput is the number of possible state transitions per second • This can also be referred to as the data rate • The signal on the right has more bits per second (bps) then the left (19 possible state changes vs. 6)

10. Telecommunications Terms • BERT – Bit Error Rate Test • BERT are disruptive tests run on a T1 to validate the integrity of the circuit (looks for errors) • CO – central office • the first hop where phone lines go • Channel bank – a device that separates a T1 into 24 individual analog phone lines

11. Telecommunications Terms • CSU/DSU – Channel Service Unit and Data Service Unit • The CSU is responsible for interfacing with the WAN service • The DSU is responsible fore interfacing with the data equipment, such as the router • The CSU typically has an RJ-45 connection from the demark point and the DSU has a V.35 connection to a router • In a CSU/DSU router card, the RJ-45 connection from the demark point goes to the router card and the connection on the card interfaces it to the router

12. Telecommunications Terms • CPE – customer premises equipment • Traditionally, the term was used to describe equipment owned by a telephone service provider that resided at customer premises, but it has evolved to include equipment owned by anyone

13. Telecommunications Terms • DACCS (pronounced dacks) – Digital Access Cross-Connect System, allows changes to the way voice channels are connected between trunks

14. Telecommunications Terms • Demarc (pronounced dee-mark) – demarcation point where the telecom provider’s responsibilities end and the customer’s begins • What is an extended demark? • Provider installed location somewhere beyond the real demarc

15. Telecommunications Terms • DS hierarchy – Digital Signal, describes the signaling rates of links

16. Telecommunications Terms • T-carrier – the generic name of digital multiplexed carrier systems in North America • T stands for trunk, since they originally designed to trunk multiple phone lines between central offices • E-carrier - The European version of digital multiplexed carrier systems • J-carrier – The Japanese version of digital multiplexed carrier systems

17. Telecommunications Terms • SONET – synchronous optical network, fiber optic system makes use of the optical carrier levels • OC1 – 51 Mbps • OC3 – 155 Mbps • OC12 – 622 Mbps • OC48 – 2,488 Mbps

18. Telecommunications Terms • ISDN – Integrated Services Digital Network • allows for the simultaneous transmission of voice and data • Uses a separate channel for signaling (Data channel or D-channel) and two remaining channels for content (Bearer channel or B-Channel) • Each B-Channel is capable of 64kbps or a total of 128kbps and the D-channel capable of 16kbps on a Basic Rate Interface (BRI) and 64kbps on a Primary Rate Interface (PRI) • A PRI is an ISDN T1 composed of 23 B-channels and 1 D-channel

19. Telecommunications Terms • LATA – local access and transport area, government defined areas in which a telecom provider can provide local services • IXC – interexchange carrier providers services to local exchanges by connecting in between LATAs • LEC – local exchange carrier, provides local service within a LATA • Local loop – the last mile connection for a circuit from a telecom facility to it destination

20. Telecommunications Terms • Latency – term used to describe the amount of time it takes for data to be processed or moved along a network • Not related to throughput, bandwidth, or speed of a link • Related to distance, speed of light, and amount of time for hardware processing • Two parts of latency – propagation delay and processing delay.

21. Telecommunications Terms • PBX – private branch exchange, used by large organizations as a localized phone company for its ability to share a limited number of public phone lines and the ability to call any internal extension number • POTS – plain old telephone service, your traditional analog phone line • Smart jack – a device that terminates a digital circuit, the service provider can perform remote testing of a circuit with the smart jack installed

22. Telecommunications Terms • RBOC – Regional Bell Operating Company • Result of the 1984 breakup of AT&T Bell System, into seven regional local only carriers • The Telecom Deregulation Act of 1996 allowed LECs (RBOCs) to sell local and long distance services. • Bell Atlantic • Southwestern Bell • Nynex • Pacific Bell • Bell South • Ameritech • US West

23. T1 Circuits • T1 circuits are full-duplex asynchronous circuits • Two Common types • Channelized T1 – voice circuit with 24 voice channels, each channel contains is own signaling information inserted into the data stream (voice) via in-band signaling • PRI – voice circuit with 24 channels, one of which is dedicated to signaling (out of band signaling), leaving 23 available voice channels

24. T1 Circuits • two types of encoding • Alternate Mark Inversion (AMI) – used for voice only • Binary Eight Zero Substitution (B8ZS) – used for data but can be used for voice

25. AMI Encoding • There are two “states” (zero and one) for the signal on the line • The mark state representing a one (+/-5 volts) and the space representing a zero (zero volts) • The next mark is always the opposite of the preceding mark • Robbed-bit signaling – every eighth bit is used to keep signal (always set to 1 regardless of original value)

26. B8ZS Encoding • introduced to resolve the shortcomings of AMI • In voice the eighth bit 1 is not an issue because you can not hear the change • In data this would change the information • Need to deal with the synchronization issue of too many zeros in a row without changing the information

27. B8ZS Encoding • if eight zeros in a row are detected in a signal, those eight zeros are converted to a pattern including intentional BPVs

28. Framing • Sample audio 8,000 times per second • Each sample is converted in to an eight-bit value • 8th bit is used for signaling (robbed-bit signaling in AMI)

29. D4/Superframe • In standard voice framing each eight-bit sample is relayed from each channel in order • each eight-bit sample is relayed from each channel in order • 8 bits X 24 channels = 192 bits • The 193rd bit is used as a framing bit • It will change this bit over 12 frames using the pattern 110111001000 • 12 frames are a superframe • Used for voice circuits

30. D4/Superframe

31. Extended Super Frame • D4/superframe standard is not practical for data transmission (lack error detection) • Extended Super frame (ESF) was developed to deal with this • Uses a pattern of 24 frames instead of 12 • Frames 4, 8, 12, 16, 20, and 24 (every fourth frame) • These frames’ framing bits are filled with the pattern 001011 • Frames 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 (every odd-numbered frame) • These frames’ framing bits are used for a new, 4,000 bps virtual data channel. This channel is used for out-of-band communications between networking devices on the link • Frames 2, 6, 10, 14, 18, and 22 (the remaining even-numbered frames) • These frames’ framing bits are used to store a six-bit CRC value for each superframe.

32. Performance Monitoring • Loss of Signal (LOS) – no electrical pulses detected (line is dead) • Out of Frame (OOF) or Loss of Frame (LOF) – a number of frames have been received with errors (synchronization invalid between two sides) • BiPolar Violation (BPV) – two mark signals occur in sequence at the same polarity (usually caused by voltage spike on the line)

33. Performance Monitoring • CRC6 - Cyclic Redundancy Check (six-bit) mechanism for error checking in ESF (check sum did not match) • Errored Seconds – shows the number of seconds in a 15-minute window in which errors on the line have occurred • Red Alarm – a local failure on the circuit or continuous OOF error • Yellow Alarm – remote alarm indication of problem down the line • Loopback test – loopback state allowing the sending of data over the link, data should return to sender exactly as sent

34. DS3 • Two types of DS3 • Channelized • 672 DS0s (28 DS1s), each capable of supporting a single POTS-line phone call • Same times referred to as a “channeled T3” • DS3 is not the same as a T3 • Clear-channel • Has no channels and is used for pure data

35. DS3 Framing • DS3 is actually a group of seven DS2s multiplexed together • Originally designed to handle phone calls • Each DS1multiplied into a DS3 has its own clocking, framing, and encoding • Multiplexing them into a DS3 can not affect this • The DS3 must also have its own clocking, framing, and encoding

36. M13 • M13 (pronounced M-one-three, not M-thirteen) is short for Multiplexed DS1 to DS3 • Requires two stages of multiplexing • M12 – multiplexed DS1 to DS2 • M23 - multiplexed DS2 to DS3 • DS3s were originally used to aggregate T1s

37. M13